1. Field of the Invention
The present invention concerns a video recorder with a doubled bandwidth of the recording track, especially for the recording and playback of HDTV signals, that is to say, for the recording and playback of signals having a frequency limit of 12 MHz with a recording-reproducing device having a limiting frequency of 6 MHz.
2. Description of the Prior Art
At the tape running speeds customary at the present time, the use of high-quality tapes and recording-reproducing heads with very fine head slits makes it possible to record video signals with a limiting frequency of 6 MHz even with video recorders of the home or semi-professional type. But if HDTV signals are to be recorded at the present state of technology and at the customary tape running speeds with such equipment of the home or semi-professional type, this will lead to obvious problems because the said HDTV signals have a limiting frequency of 12 MHz.
In the video recorder for the recording and reproduction of HDTV signals known from the German periodical "Funkschau Spezial" of 25 August 1989, pages 44 to 48, the input signal having a bandwidth of 12 MHz is scanned at a rhythm of 27 MHz and divided, line by line, into two parallel channels and fed into a digital store provided in each of the said channels. By means of these stores the signal packages are then expanded to roughly twice their original duration in time, which has the effect of halving the bandwidth of the packages. Following reconversion into analog signals and frequency modulation, the two recording signals each having a bandwidth of 6 MHz are recorded on a magnetic tape by means of a recording device with two recording-reproducing heads arranged in very close proximity to each other.
On the playback side of the known video recorder each set of recording signals recorded in two adjacent tracks is read with the help of the two closely adjacent recording-reproducing heads. Following frequency demodulation and analog/digital conversion, the reading signals obtained in this manner, each of which has a bandwidth of 6 MHz and a duration of 64 .mu.s per signal package, are again stored in digital form and are then compressed in time in the stores of the two channels, after which the compressed signal packages are combined into a playback video signal having a bandwidth of 12 MHz. When carrying out this recombination process, care must be taken to obtain a smooth transition between the signal packages at the point of junction.
It is quite evident that the known method calls for a great deal of circuitry and that additional problems are caused by the requirement that the individual signal packages should be joined together in correct phase alignment.
Accordingly, there still remains the problem of defining a video recorder capable of recording and reproducing broadband video signals, especially HDTV signals, with a recording-reproducing device having a limiting frequency of 6 MHz or, more generally, a video recorder capable of recording and reproducing broadband video signals having a limiting frequency twice as great as the highest frequency of the bandwidth of the recording-reproducing device, where the said video recorder will work in a simple and reliable manner.